Thermo-optic phase-shifting devices (e.g., thermo-optic heaters) are essential components of optical communication systems. By thermally changing the refractive index of material in an optical pathway, they can control switching, attenuation or modulation of an optical signal. The principle of operation is that by heating a waveguide, the lightwave in the waveguide can be delayed enough to control switching, attenuation or modulation thereof.
A typical thermo-optic phase shifter comprises a resistance heater thermally coupled to the high index core of a silica, or silicon, waveguide. Heat changes the temperature of the core, and thereby the refractive index since it is temperature dependent. This changes the optical refractive index and distance (optical pathlength) and hence changes the time required for the passage of the light.